Motor drive apparatus

ABSTRACT

A motor drive apparatus drives and controls a plurality of motors that rotate a common drive shaft. The motor drive apparatus includes a motor drive hardware processor that outputs equal drive power to each of the plurality of motors, and manipulates the drive power with a rotational speed detection signal of any one of the plurality of motors as a feedback signal. The feedback signal is switched based on conditions such as responsiveness and efficiency.

BACKGROUND Technological Field

The present invention relates to a motor drive apparatus.

Description of the Related Art

Conventionally, as disclosed in Japanese Patent Laid-Open Nos.2009-213190, 2003-199395 and 2003-33084, there are techniques ofrotationally driving a common load (drive shaft) by two motors. In thetechniques disclosed in the patent documents, drive power is generatedbased on signals, which are controlled respectively for two motors onthe basis of information from a sensor (encoder) that detects a rotationof the load (output shaft) for the purpose of reducing backlashes, andthe two motors are driven.

The above prior arts use two servomotors and two controllerscorresponding to the servomotors to control the gear phase into aspecific condition.

However, since the servomotors and encoder are used, the costs are high,and an installation space and a connection structure for the encoder arerequired, resulting in upsizing and complication.

In the case where a common drive shaft is rotationally driven by twomotors, if feedback systems corresponding to the respective motors areindependent of each other, torque interference occurs between themotors, the fluctuation of speed is large, and the output efficiency isdecreased.

In the case where the feedback system is configured only for one of themotors, the one motor fluctuates excessively and a drive force to theload is not stable, and the one motor has severe abrasion anddeterioration of the gear and is easily broken.

SUMMARY

The present invention has been made in view of the above problems of theprior art, and aims to achieve a smooth operation and efficient drivingby balancing a plurality of motors, while avoiding a cost increase andmechanical limitations, in driving and controlling the plurality ofmotors that rotate a common drive shaft.

To solve at least one of the above problems, according to an aspect ofthe present invention, a motor drive apparatus which drives and controlsa plurality of motors that rotate a common drive shaft, includes a motordrive hardware processor that outputs equal drive power to each of theplurality of motors, and manipulates the drive power with a rotationalspeed detection signal of any one of the plurality of motors as afeedback signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features provided by one or more embodiments of theinvention will become more fully understood from the detaileddescription given hereinbelow and the appended drawings which are givenby way of illustration only, and thus are not intended as a definitionof the limits of the present invention.

FIG. 1 is a circuit block diagram of a motor drive apparatus accordingto one embodiment of the present invention, and a schematic diagram of arotation drive mechanism with two motors;

FIGS. 2A and 2B are waveform diagrams showing rotational speedfluctuations of one motor when the two motors were activated, in whichFIG. 2A shows the fluctuation at the initial stage, and FIG. 2B showsthe fluctuation after aging degradation;

FIG. 3 is a flowchart of a control switching sequence according toswitching control example 2;

FIG. 4 is a waveform diagram according to switching control example 2,showing rotational speed fluctuations of one motor when the two motorswere activated;

FIG. 5 is a waveform diagram according to switching control example 2,showing rotational speed fluctuations of the other motor when the twomotors were activated;

FIG. 6 is a flowchart of a control switching sequence according toswitching control example 3;

FIG. 7 is a waveform diagram according to switching control example 3,showing fluctuations of rotational speed and drive power of one motorwhen the two motors were activated; and

FIG. 8 is a waveform diagram according to switching control example 3,showing fluctuations of rotational speed and drive power of the othermotor when the two motors were activated.

DETAILED DESCRIPTION OF EMBODIMENT

Hereinafter, one embodiment of the present invention will be describedwith reference to the drawings. However, the scope of the invention isnot limited to the disclosed embodiment.

As shown in FIG. 1, a motor drive apparatus 1 of the present embodimentdrives and controls two motors M1 and M2 that rotate a common driveshaft 3. For example, as shown in FIG. 1, the two motors M1 and M2 areconnected to the drive shaft 3 by a transmission mechanism in whichgears G1 and G2 fixed to output shafts of the respective motors aremeshed and connected with a gear G3 fixed to the drive shaft 3. However,this transmission mechanism is an example and is not a limitation. Forexample, a reduction gear may be added.

The drive shaft 3 and a roller 2 are coaxially integrated. The roller 2,the drive shaft 3 and the gear G3 are a common load.

The motor drive apparatus 1 includes a motor drive controller 10, and asystem controller 20.

The motor drive controller 10 includes a motor drive power amplifierthat outputs PWM-type drive power to the motors M1 and M2, and outputsequal drive power PWM to each of the two motors M1 and M2.

A rotational speed detection signal M1_FG output from the motor M1 and arotational speed detection signal M2_FG output from the motor M2 areinput to the motor drive controller 10.

The motor drive controller 10 includes a PID controller 11. A rotationalspeed detection signal which is switched by a selector 12 to therotational speed detection signal M1_FG or M2_FG of one of the twomotors is input as a feedback signal to the PID controller 11, and thePID controller 11 performs feedback control (PID control) to manipulatethe drive power PWM. The motor drive controller 10 can switch thefeedback signal between the rotational speed detection signals of thetwo motors M1 and M2 by the operation of the selector 12 according to aselection signal SEL output from the PID controller 11.

A speed command signal which specifies a target value of the feedbackcontrol (PID control) and the selection signal SEL are input to the PIDcontroller 11 from the system controller 20.

A manipulation amount (duty ratio) of the drive power (PWM) in thefeedback control (PID control) and the feedback signal (rotational speeddetection signal) are input to the system controller 20 from the PIDcontroller 11.

The system controller 20 outputs the speed command signal and theselection signal SEL to the PID controller 11 to execute drive controlof the motors M1 and M2, and also determines the selection signal SEL bycalculation processing based on information input from the PIDcontroller 11 at the time of drive control of the motors M1 and M2.Specific control examples are given below.

(1) Switching Control Example 1

In switching control example 1, switching is performed when thecumulative number of times of activation or stop of the motors M1 and M2exceeds a predetermined value.

The system controller 20 accumulates the number of times of activationof the motors M1 and M2, based on the speed command signal or thefeedback signal (rotational speed detection signal).

The system controller 20 switches the selection signal SEL when thecumulative number of times of activation of the motors M1 and M2 exceedsthe predetermined value.

That is, in the control in which the rotational speed detection signalM1_FG of the motor M1 is selected as the feedback signal, when thecumulative number of times of activation of the motors M1 and M2 exceedsthe predetermined value, the system controller 20 switches to aselection signal SEL that uses the rotational speed detection signalM2_FG of the motor M2 as the feedback signal. Accordingly, the PIDcontroller 11 inputs the selection signal SEL to the selector 12, andswitches the feedback signal to the rotational speed detection signalM2_FG of the motor M2.

Similarly, in the control in which the rotational speed detection signalM2_FG of the motor M2 is selected as the feedback signal, when thecumulative number of times of activation of the motors M1 and M2 exceedsthe predetermined value, the system controller 20 switches to aselection signal SEL that uses the rotational speed detection signalM1_FG of the motor M1 as the feedback signal. Accordingly, the PIDcontroller 11 inputs the selection signal SEL to the selector 12, andswitches the feedback signal to the rotational speed detection signalM1_FG of the motor M1.

Instead of the cumulative number of times of activation, switching maybe performed based on the cumulative number of times of stop, or thecumulative number of times of both of activation and stop.

As described above, by switching the feedback signal every fixedcumulative number of times of driving, it is possible to balance the twomotors M1 and M2 and maintain smooth and efficient driving.

(2) Switching Control Example 2

In switching control example 2, the feedback signal is switched to arotational speed detection signal which, when selected as the feedbacksignal between the rotational speed detection signals of the two motorsM1 and M2, provides better responsiveness.

The rotational speed of the motors M1 and M2 at the time of activationfluctuates as shown in FIG. 2A. As shown in FIG. 2A, speed ripplesoccur, that is, overshoot and undershoot of the rotational speed arerepeated. The amplitude of the speed ripple decreases gradually, and therotational speed converges to a target rotational speed rG.

Since load conditions change depending on aging degradation such as wearof gears, the maximum amplitude of the speed ripple increases, and asettling time T until the speed ripples converges to a certain rangeextends as shown in FIG. 2B. The settling time T is, for example, up toa time point at which the rotational speed detection signal (FG) fallswithin a predetermined convergence range rS (for example, ±5%) centeredon the target rotational speed rG, continuously for a predeterminedconvergence determination time tS (for example, 50 msec) (time point toin FIG. 2A and time point tb in FIG. 2B). The start point of thesettling time T is activation start time t0.

The system controller 20 executes the following control switchingsequence which determines a selection signal SEL by judging whether theresponsiveness is good or poor based on the length of the settling timeT. The following is an example in which the control switching sequenceis executed upon turning on the power supply, and the control switchingsequence may be executed at other time such as a standby time. Inaddition, a case where the motor drive apparatus 1 is incorporated intoa printer is given as an example. Refer to the flowchart of FIG. 3.

When the power supply is ON by turning on the main power supply of theprinter (S11), the system controller 20 activates the control switchingsequence that is one of print preparation processing (S12), and firstlycauses the rotational speed detection signal M1_FG of the motor M1 to beselected as the feedback signal by inputting a selection signal SELwhich uses the rotational speed detection signal M1_FG of the motor M1as the feedback signal to the PID controller 11 (S13).

Then, the system controller 20 inputs a speed command (target rotationalspeed) to the PID controller 11 and rotationally activates the motors M1and M2 simultaneously (S14).

The system controller 20 measures the settling time T1 visualized inFIG. 4, based on the rotational speed detection signal (FG signal)returned from the PID controller 11 (S15). The settling time T1(corresponding to a segment t0 to t1 in FIG. 4) is the settling timewhen the rotational speed detection signal M1_FG of the motor M1 is thefeedback signal.

When the measurement of the settling time T1 is finished, the systemcontroller 20 inputs a speed command (target rotational speed: 0) to thePID controller 11 and stops both of the motors M1 and M2 (S16).

Next, the system controller 20 causes the rotational speed detectionsignal M2_FG of the motor M2 to be selected as the feedback signal byinputting a selection signal SEL which uses the rotational speeddetection signal M2_FG of the motor M2 as the feedback signal to the PIDcontroller 11 (S17).

Then, the system controller 20 inputs a speed command (the same targetrotational speed as in S14) to the PID controller 11 and rotationallyactivates the motors M1 and M2 simultaneously (S18).

The system controller 20 measures a settling time T2 visualized in FIG.5, based on the rotational speed detection signal (FG signal) returnedfrom the PID controller 11 (S19). The settling time T2 (corresponding toa segment t0 to t2 in FIG. 5) is the settling time when the rotationalspeed detection signal M2_FG of the motor M2 is the feedback signal.

When the measurement of the settling time T2 is finished, the systemcontroller 20 inputs a speed command (target rotational speed: 0) to thePID controller 11 and stops both of the motors M1 and M2 (S20).

Next, if the settling time T2 is longer than the settling time T1 (YESin S21), the system controller 20 determines a selection signal whichuses the rotational speed detection signal M1_FG of the motor M1 as thefeedback signal (S22), or if the settling time T1 is longer than thesettling time T2 (NO in S21), the system controller 20 determines aselection signal which uses the rotational speed detection signal M2_FGof the motor M2 as the feedback signal (S23), and finishes the controlswitching sequence (S24). In the example shown in FIG. 4 and FIG. 5, aselection signal which uses the rotational speed detection signal M1_FGof the motor M1 as the feedback signal is determined.

The system controller 20 executes all the print preparation processingand moves into a print preparation completed state (S25).

The system controller 20 inputs the selection signal determined in stepS22 or S23 to the PID controller 11 and causes the rotational speeddetection signal according to the selection signal to be selected as thefeedback signal until the next control switching sequence is performed,and the PID controller 11 controls driving of the motors M1 and M2involved in a printing operation and the like.

As described above, by switching the feedback signal to the rotationalspeed detection signal which provides better responsiveness, it ispossible to balance the two motors M1 and M2 and maintain smooth andefficient driving.

In the above example, although the responsiveness is judged by thelength of the settling time T, a judgement may be made based on otherindex. For example, if there are one overshoot and one undershoot afteractivation, the maximum amplitude can be measured and may be used as ajudgment index. Further, if there is one overshoot after activation, anoverflow amount with respect to the target rotational speed rG can bemeasured and may be used as a judgment index.

(3) Switching Control Example 3

In switching control example 3, the feedback signal is switched to arotational speed detection signal which, when selected as the feedbacksignal between the rotational speed detection signals of the two motorsM1 and M2, has a smaller integrated value of the drive power untilreaching a target rotational speed from a predetermined rotational speed(0 in this example). Refer to the flowchart of FIG. 6. The same steps asin switching control example 2 described above are labelled with thesame reference numerals, and descriptions thereof are omitted.

As shown in FIG. 6, after step S14, the system controller 20 measures anintegrated value S1 of drive power PWM visualized in FIG. 7, based onthe manipulation amount (duty ratio) returned from the PID controller 11(S15B). The integrated value S1 corresponds to the time integrated valueof the duty ratio in a segment t0 to t3 in FIG. 7, and is the integratedvalue when the rotational speed detection signal M1_FG of the motor M1is the feedback signal.

Similarly, after step S18, the system controller 20 measures anintegrated value S2 of drive power PWM visualized in FIG. 8, based onthe manipulation amount (duty ratio) returned from the PID controller 11(S19B). The integrated value S2 corresponds to the time integrated valueof the duty ratio in a segment t0 to t4 in FIG. 8, and is the integratedvalue when the rotational speed detection signal M2_FG of the motor M2is the feedback signal.

If the integrated value S2 is larger than the integrated value S1 (YESin S21B), the system controller 20 determines a selection signal whichuses the rotational speed detection signal M1_FG of motor M1 as thefeedback signal (S22), or if the integrated value S1 is larger thanintegrated value S2 (NO in S21 B), the system controller 20 determines aselection signal which uses the rotational speed detection signal M2_FGof the motor M2 as the feedback signal (S23), and finishes the controlswitching sequence (S24). In the example shown in FIG. 7 and FIG. 8, aselection signal which uses the rotational speed detection signal M2_FGof the motor M2 as the feedback signal is determined.

Others are the same as in the above-described switching control example2.

As described above, by switching the feedback signal to the rotationalspeed detection signal which has a smaller integrated value of the drivepower, it is possible to balance the two motors M1 and M2 and maintainsmooth and efficient driving.

In the above embodiment, the number of a plurality of motors that rotatethe common drive shaft is two, but the present invention may beimplemented with three or more motors. In this case, the presentinvention may be implemented by measuring the settling time and theintegrated value of the drive power when the rotational speed detectionsignal of each of the motors is used as the feedback signal andselecting a rotational speed detection signal having the shortestsettling time or the smallest integrated value of the drive power. Thepresent invention may also be implemented in a manner similar to theabove-described embodiment by randomly selecting two out of three ormore rotational speed signals every time the control switching sequenceis executed.

According to the embodiment of the present invention, equal drive poweris output to each of a plurality of motors, and the drive power ismanipulated using the rotational speed detection signal of any one ofthe plurality of motors as the feedback signal. Therefore, an encoderfor detecting a rotation of the common drive shaft is not necessary, asmooth operation is achieved with equal drive power, and driving can beefficiently performed by balancing the plurality of motors.

Further, by switching the feedback signal between the rotation detectionsignals of the plurality of motors, smooth and efficient driving can bemaintained.

Although the embodiment of the present invention has been described andillustrated in detail, the disclosed embodiment is made for purposes ofillustration and example only and not limitation. The scope of thepresent invention should be interpreted by terms of the appended claims.

The entire disclosure of Japanese Patent Application No. 2018-149001,filed on Aug. 8, 2018, is incorporated herein by reference in itsentirety.

What is claimed is:
 1. A motor drive apparatus that drives and controlsa plurality of motors that rotate a common drive shaft, the motor driveapparatus comprising a motor drive hardware processor that outputs equaldrive power to each of the plurality of motors, and manipulates thedrive power with a rotational speed detection signal of any one of theplurality of motors as a feedback signal.
 2. The motor drive apparatusaccording to claim 1, wherein the feedback signal is switchable betweenrotational speed detection signals of the plurality of motors.
 3. Themotor drive apparatus according to claim 2, comprising a hardwareprocessor that, in response to a cumulative number of times ofactivation and/or stop of the plurality of motors exceeding apredetermined value, switches the feedback signal between the rotationalspeed detection signals of the plurality of motors.
 4. The motor driveapparatus according to claim 2, comprising a hardware processor thatswitches the feedback signal to a rotational speed detection signalwhich, when selected as the feedback signal out of the rotational speeddetection signals of the plurality of motors, provides betterresponsiveness.
 5. The motor drive apparatus according to claim 2,comprising a hardware processor that switches the feedback signal to arotational speed detection signal which, when selected as the feedbacksignal out of the rotational speed detection signals of the plurality ofmotors, has a smaller integrated value of the drive power until reachinga target rotational speed from a predetermined rotational speed.